Generally, the idea is that once nominated, you either donate, or do the challenge as a forfeit if you can't/don't donate. You can chose to do both, and it's great if you do. But remember, getting the word out can be just as good as a donation, so people shouldn't feel bad if they don't donate, and also, others shouldn't shame them for it.

Although, I do see the point of people doing it "just because" they get nominated, without even knowing about the reasons. I've seen video after video of people doing the challenge with no mention of the phrases "donate" or "ALS".